The present invention relates to composite containers, and in particular relates to composite containers for vacuum packaging fragile products, such as potato crisps or cookie biscuits, and associated methods.
Food and drink products and other perishable items are often packaged in tubular containers that are sealed at both ends. For some time, it has been recognized that substantial economies, as well as environmental advantages, can be realized by the use of composite containers, as opposed to the traditional glass and metal containers. These composite containers typically include at least one structural body ply made of paperboard and are formed by wrapping a continuous strip of the body ply material around a mandrel of a desired shape to create a tubular structure. At the downstream end of the mandrel, the formed tube is cut into discrete lengths and fitted with end closures to form the container.
Tubular containers of this type typically include a liner ply on the inner surface of the paperboard body ply. The liner ply prevents liquids from leaking out of the container and also prevents liquids from entering the container and possibly contaminating the food product contained therein. Preferably, the liner ply is also resistant to the passage of gasses so as to prevent odors of the food product in the container from escaping and to prevent atmospheric air from entering the container through the liner and spoiling the food product. The liner ply is often a laminate including kraft paper, aluminum foil and/or one or more polymer layers. Thus, the liner ply provides barrier properties and the body ply provides structural properties for the composite container. In addition, a label ply is typically adhered to the outer surface of the paperboard body ply.
Certain food products benefit from being packaged while under a vacuum. Vacuum packaging removes oxygen from the space surrounding the product, which can improve the shelf life of the product within the package. This is especially true for perishable food products, or food products that may become stale if exposed to air. However, it is generally recognized that vacuum packaging in some tubular containers can only be accomplished with difficulty, if at all. Because of the structural design of the composite container, the application of vacuum to the interior of the container often results in partial or complete inward collapsing of the container walls along the length of the container. This can result in an unacceptable appearance for the composite container or an unacceptable sealing of the product within the container.
This problem is further discussed in U.S. Pat. No. 4,158,425, assigned to the assignee of the present invention and incorporated herein by reference. To avoid the partial or complete collapsing of the paperboard body ply of the container upon application of a vacuum inside the container, the container according to the ""425 patent has an impermeable or hermetically sealed liner secured interiorly to the container body solely at the opposed ends thereof with the major length of the liner being free of the tubular body so as to allow an inward contracting of the liner without the introduction of excessive stresses to the container body itself. A vacuum or reduced pressure atmosphere within the liner causes an inward deformation of the liner into contact with the product substantially independently of the surrounding container body. Thus, the stresses which are transferred to the container body are at the opposed ends thereof which are in turn structurally supported by a pair of conventional end closures.
The ""425 patent, however, only addresses the problem of collapsing of the container walls. The ""425 patent does not discuss or provide a container designed to secure the food products during transportation or to prevent breakage of the food products during packaging. In particular, fragile food products, such as potato crisps or cookie biscuits, are extremely susceptible to breakage during transportation and packaging. These types of products are typically stacked within the container such that the products can move about the container. Although the ""425 patent provides an inwardly moving liner, it is directed to sealing the product for freshness without damaging the tubular body, and not directed to providing cushioning support to the food products in order to prevent damage during transportation and packaging.
The problem of securing food products during transportation is addressed in co-pending application Ser. No. 09/543,439 entitled xe2x80x9cContainer and Method for Making Container for Fragile Products,xe2x80x9d assigned to the assignee of the present invention and herein incorporated by reference. The container disclosed by the Ser. No. 09/543,439 application includes a flexible end closure secured to at least one of the opposed ends of the container that is free to move inwardly against food products contained therein when a vacuum is applied so as to provide cushioning support to the food products. As such, the food products are supported by a xe2x80x9cpillow-likexe2x80x9d cushion instead of a metal end closure or other rigid surface as provided by current containers. Despite the advantages provided by the flexible end closure disclosed by the Ser. No. 09/543,439 application, certain food products still suffer from breakage during the packaging process, particularly those products that are vacuum packed. In particular, it is believed that the vacuum packaging process causes the flexible end closure to move rapidly inward against the adjacent fragile products within the container, causing the products located near the end closure to be broken. Seeing broken cookies or potato crisps when the container is opened is very undesirable from a consumer standpoint and may lessen consumer appeal for the food products.
A conventional process for packaging food products includes sealing a flexible end closure, such as a membrane, to one end of the tubular container, inverting the container with the flexible end closure attached thereto, and depositing the products within the tubular container such that the products first deposited into the container rest against the inner surface of the flexible end closure. The remaining food products are then stacked upon one another until the container is sufficiently full. The filled container is placed inside a vacuum chamber and the chamber is depressurized to create a vacuum. The open end of the tubular container is then closed while the container and its contents are subjected to the vacuum. The vacuum chamber is then repressurized, which causes the flexible end closure of the sealed tubular container to move rapidly inward towards the food products. This rapid movement of the flexible end closure acts against the weight of the stacked food products that are resting against the inner surface of the flexible end closure. As such, the rapid movement of the flexible end closure results in a sharp pressing force against the food products, particularly against the food products adjacent the flexible end closure. The pressing force often results in breakage of the food products adjacent the flexible end closure, as these food products receive the brunt of the pressing force from the flexible end closure.
Accordingly, there is a need in the industry for a container that hermetically seals perishable food products, but that is also capable of protecting fragile food products during packaging, and particularly capable of preventing breakage of the food products located adjacent the end closures. At the same time, however, such a container would also be capable of withstanding the rigors of vacuum packaging so as to increase the shelf life of the product and provide other benefits attendant to vacuum packaging.
These and other needs are provided, according to the present invention, by a tubular container having an overcap secured to at least one of the opposed ends of the container that defines a bias member for biasing a membrane-type flexible end closure or lid inwardly towards the food products before a vacuum is applied. The bias member also displaces the food products so that the flexible lid can move inwardly without exerting significant force on the food products. As such, the rapid and excessive movement of the flexible lid during conventional vacuum packaging is avoided, thus preventing the breakage of the food products located adjacent the flexible lid.
In particular, the tubular composite container for vacuum packaging products, such as potato crisps, cookie biscuits, baked wafers or the like, includes a tubular body ply formed of a paperboard material having inner and outer surfaces and opposed ends. At least one end of the body ply is rolled outwardly to form a rim. The tubular body is formed using conventional spiral winding techniques known in the art, such as described in U.S. Pat. No. 4,185,425, which is assigned to the assignee of the present invention and incorporated herein by reference.
The tubular composite container also includes a flexible membrane-type end closure or lid that is positioned against the rim and sealed thereto. The flexible lid moves inwardly against the products contained within the tubular body when a vacuum is applied so as to provide cushioning support for the products. In one embodiment, the flexible lid includes a foil layer that is impervious to the passage of liquids and gasses.
Advantageously, the tubular composite container also includes an overcap attached to the container adjacent the flexible lid. The overcap defines a bias member for biasing the lid inwardly towards the food products before a vacuum is applied. In one embodiment, the bias member comprises at least one rib, which may have a thickness substantially equal to the base portion of the overcap. In another embodiment, the bias member has a tubular shape. In yet another embodiment, the bias member has a frustoconical shape. The bias member can be formed by profiling or shaping the surface of the overcap, which in one embodiment gives the overcap a concave outer surface and convex inner surface. The bias member can also be formed by providing a rib or other shape extending from the inner surface of the overcap so that the outer surface remains substantially planar.
Associated methods also form a part of the invention and, according to one embodiment, include the steps of attaching a flexible lid to at least one of the opposed ends of a tubular body member, biasing the flexible lid inwardly with a bias member, and depositing one or more products inside the tubular body member. The vacuum packaging operation can then be performed by creating a vacuum or negative pressure inside a chamber storing the open tubular body and then closing the open end of the tubular body. The negative pressure created inside the chamber is then released such that the flexible lid can move inwardly towards the food products. However, because the flexible lid is substantially biased inwardly by the bias member before the vacuum packaging operation is performed, the flexible lid undergoes substantially less inward movement when the vacuum is released inside the chamber, thereby reducing breakage to the food products located adjacent the flexible lid. In one preferred embodiment, the bias member is incorporated into the overcap, although the bias member can have other configurations.
Accordingly, and as is explained in more detail below, the Applicants have provided a new container for vacuum packaging products which overcomes the disadvantages of conventional containers. The container and method of the present invention is particularly advantageous for food products that are easily damaged during packaging, such as potato crisps or cookie biscuits, although other fragile products, such as electronics and the like, can also be stored in the container of the present invention. The new container is easy to open for consumers, and can use conventional construction techniques. At the same time, however, the present container is capable of withstanding the rigors of vacuum packaging so as to maintain a rigid shape and provide a hermetically sealed container to prevent air and moisture from contaminating the products contained therein.